President Donald Trump on Thursday launched a long-promised commission on "election integrity," rekindling a controversy over the prevalence of voter fraud at U.S. polls.

The commission, established by executive order, is the upshot of Trump's unsubstantiated claim shortly after taking office that more than 3 million undocumented immigrants illegally voted in November's election.

White House aides said the scope of the commission, chaired by Vice President Mike Pence, will reach beyond allegations of voter fraud to include voter suppression and other suspect election practices, and would include members from both major political parties.

"The president's committed to the thorough review of registration and voting issues in federal elections," White House principal deputy press secretary Sarah Sanders told reporters Thursday. "And that's exactly what this commission is tasked with doing."

But that did little to quell criticism from many of the same parties who lambasted Trump for his January claims. Voting rights groups and several prominent Democrats charged Thursday that Trump's commission was both unnecessary - calling claims of voter fraud wildly overblown - and an attempt to divert attention from his firing of FBI Director James Comey.

Michael Waldman, president of the Brennan Center for Justice, called the commission "a sham and distraction," alleging that Trump was trying "to pivot" from the firestorm that followed his firing of Comey while he was leading an investigation into meddling in the U.S. election by Russia.

"He fired the person investigating a real threat to election integrity, and set up a probe of an imaginary threat," Waldman said.

League of Women Voters President Chris Carson said, "the real purpose of this effort is to justify President Trump's false claims of widespread voter fraud in the 2016 elections." She said the commission was being filled with "political ideologues with dangerous agendas."

In a statement before Trump signed his order, New York state attorney general Eric Schneiderman, D, said that "no matter how many times President Trump claims otherwise, voter fraud is an imaginary problem." Schneiderman said his office found no substantiated claims of voter fraud in New York last year.

Numerous studies have shown that instances of in-person voter fraud are rare and The National Association of Secretaries of State, which represents many of the country's state elections officials, said in January that it is "not aware of any evidence that supports the voter fraud claims made by President Trump."

Kansas Secretary of State Kris Kobach, who has aggressively pursued allegations of voter fraud in his state, will serve as vice chairman of the commission, the White House announced, further fueling the controversy over its formation.

Kobach is the only secretary of state with the authority to prosecute voter fraud, and he has helped create some of the nation's strictest voter ID requirements.

In a Fox News interview in February, Kobach said there were 115 cases in Kansas of noncitizens on the voter rolls or trying to get on the voter rolls, which he said could be the "tip of the iceberg." More than 1.7 million people are registered to vote in Kansas.

Last month, Kobach got his first conviction of a noncitizen who illegally voted in a Kansas election without being a U.S. citizen. It was his eighth voter fraud conviction since getting the power to pursue such cases in 2015.

Kobach first entered the national spotlight when he advised GOP presidential nominee Mitt Romney on the idea of "self-deportation" for illegal immigrants during the 2012 presidential campaign. Before that, he had written Arizona's strict 2010 "show-me-your-papers" immigration law and Alabama's tough immigration enforcement laws.

It was also Kobach who helped design President George W. Bush's registration system for "higher risk" immigrants, which required fingerprinting and interrogations upon arrival. He later helped lead the fight against President Barack Obama's executive actions on immigration.

Along with immigration issues, Kobach has also became a major figure in the national conservative movement to add more requirements for Americans to vote or register to vote. Since the Supreme Court struck down in 2013 a key part of the Voting Rights Act, Kobach has been at the center of many legal skirmishes over voting requirements nationwide.

The White House said the Presidential Advisory Commission on Election Integrity - which is slated to deliver a report to Trump next year - would include perhaps another dozen members.

Those already on board include: Indiana Secretary of State Connie Lawson, R; New Hampshire Secretary of State Bill Gardner, D; Maine Secretary of State Matthew Dunlap, D; Christy McCormick, commissioner of the election assistance commission; and former Ohio secretary of state Ken Blackwell, R.

The genesis of the commission came during Trump's first days in office. During a private Jan. 23 meeting with top congressional leaders, the president claimed that between 3 million and 5 million undocumented immigrants illegally voted in November's election.

He later reiterated the claim. "They all voted for Hillary. They didn't vote for me," Trump said in an interview with ABC News that aired Jan. 25. "I don't believe I got one."

In defending his claim, for which the White House has yet to provide documentation, Trump announced he would issue an executive order related to voter fraud, and Pence told Republicans that the administration would "initiate a full evaluation of voting rolls."

Since then, there has been more ammunition for critics who say the exercise is aimed at a problem that isn't widespread.

A recent investigation in North Carolina by the state board of elections there found that of the 4.8 million voters who participated in last year's election, 508 were not eligible to vote.

The investigation concluded that "no races - statewide or local - would have had a different outcome than the one already certified" if the improper votes were removed.

Most of those who shouldn't have voted - 441, according to a report on the investigation - were convicted felons, many on probation. In North Carolina, felons can only vote after serving their sentences, including probation.

The investigation also found 41 noncitizens had voted, 24 people had voted twice and two people falsely voted using the name of a recently deceased family member.

The state board in North Carolina said not every instance noted in the report was necessarily voter fraud because in many cases there was no intent to do anything wrong. In one case, local prosecutors have already decided not to bring charges.

That involved a woman who impersonated her dead mother - whom she told investigators was a "tremendous Donald Trump fan" - at the polls.

In an email, the daughter told investigators that her 89-year-old mother had told her "if anything happens, you have my power of attorney, and you be sure to vote for Donald Trump for me."

The Washington Post's Sari Horwitz and Robert Barnes contributed to this report.